Talking about the display function of LED screen
2023-10-12 04:09:23
Since the luminescent color and luminous efficiency of the LED are related to the materials and processes for producing the LED, three kinds of red, green, and blue are widely used at present. Because the LED operating voltage is low (only 1.5-3V), it can actively emit light and have a certain brightness, the brightness can be adjusted with voltage (or current), and it is shock-resistant, vibration-resistant, and long-lived (100,000 hours). Among the display devices, there is currently no other display mode that matches the LED display mode.
A display screen made by putting together red and green LEDs as a pixel is called a two-color screen or a color screen; a display screen in which three LED tubes of red, green, and blue are put together as a pixel is called a three-color screen or a full-color screen . The pixel size of the indoor LED screen is usually 2-10mm. It is often used to package several LED dies that can produce different basic colors. The size of the outdoor LED screen is 12-26mm, and each pixel contains several pixels. A variety of monochrome LED components, the common product is called the pixel tube, two-color pixel tube is generally composed of 3 red 2 green, three-color pixel tube with 2 red 1 green 1 blue.
Regardless of whether a single-color, two-color, or three-color screen is fabricated with LEDs, the brightness of each LED that constitutes a pixel must be adjusted to display an image. The fineness of the adjustment is the order of the grayscale of the display screen. The higher the gray scale, the finer the displayed image, the richer the color, and the more complex the corresponding display control system. Generally, the color transition of the 256 gray-scale images is very soft, and the color transitions of the 16-step gray scale are very obvious. Therefore, color LED screens are currently required to be made up to 256 grey levels.
There are two ways to control the brightness of the LED. One is to change the current flowing through the LED. Generally, the LED tube allows the continuous operating current to be around 20 mA. Except that the red LED has saturation, the brightness of other LEDs is basically proportional to the current flowing through; the other method is to use The visual inertia of the human eye uses pulse width modulation to achieve gray-scale control, that is, to periodically change the width of the light pulse (ie, duty cycle) as long as the period of this repeated lighting is short enough (ie, the refresh rate is high enough). The eye can't feel the jitter in the pixels. Since pulse width modulation is more suitable for digital control, in today's widespread use of computers to provide LED display content, almost all LED screens use pulse-width modulation to control the gray-scale equivalent.
LED control system usually consists of three main parts: main control box, scan board and display and control device. The main control box obtains brightness data of each pixel of a screen pixel from the display card of the computer, and then re-assigns to a plurality of scanning boards. Each scanning board is responsible for controlling several rows (columns) on the LED screen, and each row (column) is The LED display signal is transmitted serially. Currently, there are two ways to serially transmit the display control signal: one is to centrally control the grayscale of each pixel on the scanning board, and the scanning board decomposes the luminance values ​​of the pixels in each row from the control box (ie, pulse width modulation), and then The open communication number of each row of LEDs is transmitted in pulse form (lighting 1 and not lighting 0) to the corresponding LED in a serial manner and controlling whether it is lit or not. This method uses fewer devices, but the amount of data transmitted in series is large because each pixel requires 16 pulses at 16 gray levels and 256 gray levels at a period of one repeating light. Pulses, due to device operating frequency limitations, generally only allow the LED screen to achieve 16 gray levels.
Another method is that the content of the scan board serial transmission is not a switching signal of each LED but an 8-bit binary luminance value. Each LED has its own pulse width modulator to control the lighting time. In this way, in a repetitively lit period, each pixel needs only 4 pulses under 16 gray scales and only 8 pulses under 256 gray scales, which greatly reduces the serial transmission frequency. Using this method of decentralized control of LED grayscale can easily achieve 256 gray-scale control.
A display screen made by putting together red and green LEDs as a pixel is called a two-color screen or a color screen; a display screen in which three LED tubes of red, green, and blue are put together as a pixel is called a three-color screen or a full-color screen . The pixel size of the indoor LED screen is usually 2-10mm. It is often used to package several LED dies that can produce different basic colors. The size of the outdoor LED screen is 12-26mm, and each pixel contains several pixels. A variety of monochrome LED components, the common product is called the pixel tube, two-color pixel tube is generally composed of 3 red 2 green, three-color pixel tube with 2 red 1 green 1 blue.
Regardless of whether a single-color, two-color, or three-color screen is fabricated with LEDs, the brightness of each LED that constitutes a pixel must be adjusted to display an image. The fineness of the adjustment is the order of the grayscale of the display screen. The higher the gray scale, the finer the displayed image, the richer the color, and the more complex the corresponding display control system. Generally, the color transition of the 256 gray-scale images is very soft, and the color transitions of the 16-step gray scale are very obvious. Therefore, color LED screens are currently required to be made up to 256 grey levels.
There are two ways to control the brightness of the LED. One is to change the current flowing through the LED. Generally, the LED tube allows the continuous operating current to be around 20 mA. Except that the red LED has saturation, the brightness of other LEDs is basically proportional to the current flowing through; the other method is to use The visual inertia of the human eye uses pulse width modulation to achieve gray-scale control, that is, to periodically change the width of the light pulse (ie, duty cycle) as long as the period of this repeated lighting is short enough (ie, the refresh rate is high enough). The eye can't feel the jitter in the pixels. Since pulse width modulation is more suitable for digital control, in today's widespread use of computers to provide LED display content, almost all LED screens use pulse-width modulation to control the gray-scale equivalent.
LED control system usually consists of three main parts: main control box, scan board and display and control device. The main control box obtains brightness data of each pixel of a screen pixel from the display card of the computer, and then re-assigns to a plurality of scanning boards. Each scanning board is responsible for controlling several rows (columns) on the LED screen, and each row (column) is The LED display signal is transmitted serially. Currently, there are two ways to serially transmit the display control signal: one is to centrally control the grayscale of each pixel on the scanning board, and the scanning board decomposes the luminance values ​​of the pixels in each row from the control box (ie, pulse width modulation), and then The open communication number of each row of LEDs is transmitted in pulse form (lighting 1 and not lighting 0) to the corresponding LED in a serial manner and controlling whether it is lit or not. This method uses fewer devices, but the amount of data transmitted in series is large because each pixel requires 16 pulses at 16 gray levels and 256 gray levels at a period of one repeating light. Pulses, due to device operating frequency limitations, generally only allow the LED screen to achieve 16 gray levels.
Another method is that the content of the scan board serial transmission is not a switching signal of each LED but an 8-bit binary luminance value. Each LED has its own pulse width modulator to control the lighting time. In this way, in a repetitively lit period, each pixel needs only 4 pulses under 16 gray scales and only 8 pulses under 256 gray scales, which greatly reduces the serial transmission frequency. Using this method of decentralized control of LED grayscale can easily achieve 256 gray-scale control.
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